In filter devices, contaminated fluid can be guided through a feed line into a filter pot incorporating the filter element, flowing from the outside inward through the filter element. In this manner, the polluting material particles are separated from the fluid. Cleaned in this manner, the fluid proceeds from the inside chamber of the filter element and through the associated drain from the filter housing to the use point in the hydraulic or other fluid circuit which is being supplied with clean fluid.
After an extended period of time in use, such filter element becomes contaminated, and must be replaced with a new, clean filter element. For this purpose, the filter pot with the filter element arranged therein is screwed or threaded out of the housing and then removed according to conventional practice. During this unscrewing step, the element holder is usually moved radially along with the filter element. The packing or sealing ring provided between element holder and housing can be damaged in the process. Especially in the reverse situation, following exchange of the filter element and replacement of the filter pot in the housing by screwing in and out, crushing, drilling and sliding movements may occur in the packing ring. Such movements tend to negatively influence the sealing effect of the packing ring, so that unfiltered fluid can become mixed with already filtered fluid.
During the exchange process the filter pot is filled with fluid, such as hydraulic oil, liquids which are flame-resistant, biologically decomposable liquids or polluted water. Frequently fluid leaks out inadvertently into the environment and leads to pollution of the environment. Such pollution occurs most often when the exchanging filter elements in working machinery located outside.
The filter devices disclosed in German Patent No. 30 31 431 C2 and German unexamined publication 26 23 409 have closing arrangements constructed as reflux check valves of elastomeric material. A valve in the form of a one-part flange member surrounds the element holder for the filter element. As soon as fluid is fed in through one of the connections, in the form of a feed line, the elastically flexible flange-like valve opens. Otherwise, the valve is held in its closed position because of its elasticity, and prevents undesired fluid discharge into the atmosphere through the connection or when the filter pot is removed out of this assembly. No closing of the fluid-carrying connections in the housing of the device is provided. The known closing devices require considerable structure space in the area of the element holder and do not always function reliably during operation. Especially with the pressure peaks in the connections or even in the case of an undesired reversal of the fluid flow direction, an inversion or tearing apart of the plate- or disk-like elastomeric sealing border of the flange part can cause the closing arrangement to become unserviceable. This last occurrence leads to breakdown of the filter device.